Issues getting ZF10M into ahead.

[fergycool]

I’ve got some ongoing issues with a ZF10m gearbox.

In reverse/astern it works fine. The gear clunks and the prop spins fine.

However, when I move into forward/ahead it clunks, then spins at about 150 rpm for between 5 to 30 seconds then there’s another clunk and the propshaft starts spinning at about 400rpm. Engine revs are about 750 at idle, so that matches the 1.86:1 reduction ratio (well it does if you consider I was using one of those crappy handheld optical rev counters for the shaft). Once it’s properly spinning it stays that way.

Ahead is position B = 1.86:1, Astern is position A 2.06:1

- I’ve removed the control cable and tried changing gear manually (i.e. my hand on the gearbox level) when in idle. That exhibits the same symptoms.
- The ATF is fine. I change it fairly regularly and it’s clear and the right level.

I had similar problems with my other gearbox (ZF15) where it just did not move in forward at all. However, that failed pretty quickly. Whereas this gearbox has been in the same state for quite a few hours.

I know there are many threads about the Hurth and ZF gearboxes and slipping discs in forward, but this seems different. Is it?

Is a new gearbox or rebuild in my future?

Thanks
Ferg

 

[fergycool]

I’ve come across a flowchart, on a different forum, that suggests for delayed engagement/Slippage under power,

- to drain and fill the gearbox with 1 litre of diesel
- Run engine in idle for 3 mins with engaging f/r at 10 second intervals
- Stop engine and drain diesel
- Replace with correct amount of ATF

http://www.cruisersforum.com/forums/f114/hurth-zf10-slipping-59418.html

Is this just alternative medicine for gearboxes (i.e. it does not work but might make me feel better), or is there any valid reason for doing something like this?

 

[Adamastor]

When you drain the gearbox, check the fluid for discolouration.
Sounds like you may have bent a fork.

 

[fergycool]

Well i gave the “diesel flush” a go. I emptied the ATF and filled with 0.5l of diesel. I ran in idle for 1min changing into forward and reverse a few times. With the gearbox full of diesel it goes into gear immediately. I've never had such a responsive box

I drained the tank and refilled with the right volume of ATF (0.35l).

It has made a slight difference, but not much to be honest.

I think a new, and better, gearbox is on to buy list. I need to calculate by how much I need to move the propshaft and lift the engine to replace the ZF10m with a ZF15.

 

[fergycool]

When you drain the gearbox, check the fluid for discolouration.
Sounds like you may have bent a fork.

I guess fixing a bent fork is a strip down job?

 

[BigWelshPirate]

Have there been any updates to this forum recently?